U.S. Pat. No. 4,912,011 discloses a light-sensitive material comprising a support and a light-sensitive layer provided thereon which contains silver halide, a reducing agent, a polymerizable compound and a color image forming substance. The silver halide, the reducing agent, the polymerizable compound and the color image forming substance are contained in microcapsules (light-sensitive microcapsules) which are dispersed in the light-sensitive layer. The U.S. Patent corresponds to Japanese Patent Provisional Publications No. 61(1986)-275742 and No. 61(1986)-278849 and European Patent Provisional Publication No. 0203613A.
An image forming method using the light-sensitive material is also disclosed in U.S. Pat. No. 4,912,011. The method comprises the steps of imagewise exposing the light-sensitive material, and heating the light-sensitive material. A latent image of the silver halide is formed by the exposure. The polymerizable compound is polymerized by heating within the area where the latent image has been formed. The light-sensitive material is then pressed on an image-receiving material to transfer the unpolymerized polymerizable compound with a color image forming substance to the image-receiving material to form a color image on the image-receiving material.
Further, a method of polymerizing the polymerizable compound within the area where the latent image of the silver halide has not been formed is disclosed in Japanese Patent Provisional Publications No. 61(1986)-243449, No. (1986)-260241, No. 2(1990)-141756 and No. 2(1990)-141757. The contents of the former two publications are described in European Patent Provisional Publication No. 0202490A.
The heating time for the development and polymerization reactions was usually from 1 second to 5 minutes, and preferably from 5 seconds to 1 minutes, as is described at column 23, lines 24-26 in U.S. Pat. No. 4,912,011. Various heating means are disclosed at column 22, line 24 to column 23, line 13 in U.S. Pat. No. 4,912,011. The light-sensitive material can be heated from the side of the support or from the side of the light-sensitive layer (cf., column 23, lines 10-13 in U.S. Pat. No. 4,912,011).
By the way, an image recording apparatus for the above-described image forming method has recently been proposed (cf., U.S. Pat. Nos. 4,737,822, No. 4,783,683, No. 4,797,710, No. 4,819,032 and No. 4,825,041). The size of the apparatus is proportional to the heating time as well as the size of the light-sensitive material. Accordingly, the heating time for the development and polymerization reactions should be shortened to construct a compact apparatus.
Further, the light-sensitive material used in the apparatus is preferably in the form of roll film. The roll of the light-sensitive material is continuously imagewise exposed to light, heated and pressed on an image-receiving material. In this case, the length of the light-sensitive material necessary for formation of one image is determined by the time of the longest process, namely the heating process. Accordingly, it is necessary for saving the roll of the light-sensitive material to shorten the heating time.
There are two ways to shorten the heating time. One way is to improve the light-sensitive material. The other is to improve the heating means.
The development and polymerization reactions smoothly proceed in alkaline conditions. Therefore, the light-sensitive material preferably contains a base precursor as an image formation accelerator to shorten the heating time. In order to more accelerate the development and polymerization reactions, it is preferred to incorporate the base precursor into light-sensitive microcapsules, as is described in U.S. Pat. No. 4,939,064 (corresponding to Japanese Patent Provisional Publication No. 64(1989)-32251 and European Patent Provisional Publication No. 0301539A) and Japanese Patent Provisional Publications No. 1(1989)-263641, No. 2(1990)-14601 and No. 3(1991)-25444. The base precursor is composed of a salt of an organic base with a carboxylic acid, and is generally used in the form of solid particles.
With respect to the heating means, the efficiency of heat conduction has mainly been considered. Accordingly, the light-sensitive material has been directly heated from the side of the light-sensitive layer in the case that the heating time should be shortened.